Devices for the thermal coating of a surface are described in U.S. Pat. Nos. 6,372,298 B1, in 6,706,993 B1 and in WO 2010/112567 A1. All of the devices have: a wire supply unit for the supply of a wire, wherein the wire acts as a first electrode; a source for plasma gas for generating a plasma gas stream; a nozzle body with a nozzle opening through which the plasma gas stream is conducted as a plasma gas jet to one wire end; and a second electrode which is arranged in the plasma gas stream before the latter enters into the nozzle opening.
An are forms between the two electrodes through the nozzle opening. Said arc also forms the plasma gas flowing through the nozzle opening. The plasma gas jet emerging from the nozzle opening impinges on the wire end and, there, with the arc, causes the wire to melt and causes the melted wire material to be transported away in the direction of the surface to be coated. Annularly around the nozzle opening there are mounted secondary air nozzles by means of which a swirling secondary gas jet is generated, which secondary gas jet impinges, downstream of the wire end, on the material that has melted off the wire end, and which secondary gas jet thus effects an acceleration of the transport in the direction of the surface to be coated and a secondary atomization of the melted wire material.
The coating should be produced without significant inclusions of non-melted or only partially melted spray particles. Such inclusions or so-called spatter are generally formed by incompletely melted wire material. It has been found that, if the wire is to be melted as completely and uniformly as possible, precise positioning of the wire relative to the nozzle opening is necessary. Likewise, even a very short operating time of the device in the coating mode can necessitate a new alignment of the wire position.